The present invention relates to process and apparatus for the production of a uniform flow of particles discharged over the width of a hopper, for example, fibers consisting of cellulose-containing or mineral-containing materials or fibers, chips or mixtures of such particles provided with binders for the production of boards from these materials. A hopper is charged with these materials by a feeding device arranged above the hopper transversely to the longitudinal axis of the hopper, and a stationary feed arranged to one side of the hopper supplies the feeding device with particles.
In the production of boards from glue-coated chips, so-called chip boards or for the production of boards consisting of wood fibers or paper fibers or boards consisting of mixtures of cellulose fibers and chips in which water and gypsum are added as a binder, it is necessary that these particles be stored in hoppers before the production of such boards. The main reason for storage in hoppers is that in the continuous production of webs from these particles, a uniform amount of these particles must always be on hand to prevent defects, such as defects in the specific gravity or in the density, for example.
With this type of intermediate storage, it must also be kept in mind that material stored for the same length of time must be supplied for further processing, in particularly, when this relates to glue-coated chips for the production of chip boards or when this relates to the production of MDF (Medium Densitive Fibers), which also have already been glue-coated for the production of MDF boards. In order to achieve this goal, the so-called first-in first-out principle of storing in hoppers must be employed. If particles are to be mixed in a hopper, for example, cellulose fibers mixed with wood chips, a first-in first-out storage is not suitable since the particles of each type must be stored above each other and then scraped by removal of the front wall of material with scraper rolls. A thorough mixing is obtained with the movement of the bottom belt of the hopper against the scraper rolls.
With intermediate storage in hoppers it is generally necessary to make sure that patches having a higher density, so-called pockets, do not occur within the stored particles, and that the upper particle layer does not have irregularities transversely and longitudinally to the longitudinal axis of the hopper. This prevents defects from occurring in the composition and in the material amounts by scraping with the scraper rolls. To even out the upper layer, a so-called back stripper is used in the upper region of the hopper which extends over the entire width of the hopper and of which the forward moving leg turns in a direction opposite to the forward moving leg of the bottom belt.
DE-PS 30 31 864 discloses a process and an apparatus for charging an intermediate hopper. Essentially following a feeding command emanating from the hopper and a signal of the amount of material in the hopper to be supplemented, a uniformly distributed chip supply is continuously provided above the hopper corresponding to the hopper width. The chips are then discharged into the hopper. A screw conveyor extending over the entire width of the hopper is especially suitable and after proper refilling with a chip supply, the screw conveyor releases these chips over the entire width of the hopper via a discharge slot in a movable trough. Such a device used with particles inclined to lump together in the preparation for a uniform discharge has a tendency to compact the particles together. Sticking of the particles to the transport means also occurs. With particle discharge over the entire width of the hopper there is no guarantee that evenly distributed material remains present in the hopper. The risk of pocket formation also exists.
DE-PS 952 565 relates to a device for providing uniform deliveries of wood chip material or other bulk material resulting in uniformity with a discharge device known per se which takes material arriving in an even flow and throws the material in the same or opposite direction as movement of the delivery support. The device is narrow and moves back and forth over the delivery width. With such a discharge service a uniform deposit in a hopper in the direction of and transversely to its longitudinal axis cannot be obtained since the material arriving via a conveyor belt is separated by the influence of the discharge device. In some areas, as explained with the example of wood chips, only large wood chips or heavy chips are deposited. In other areas transversely to the longitudinal axis of the hopper only small or light particles are deposited. In this disclosure, another feed is also described whereby particles to be deposited are discharged via a pivotable pipe. However, as a result of their discharge speed, the particles are also deposited separately according to size and weight.